Re: [RFC] delayed allocation for ext4

From: Alex Tomas
Date: Thu Dec 28 2006 - 23:57:14 EST

>>>>> David Chinner (DC) writes:

DC> So that mean's we'll have 2 separate mechanisms for marking
DC> pages as delalloc. XFS uses the BH_delay flag to indicate
DC> that a buffer (block) attached to the page is using delalloc.
>> well, for blocksize=pagesize we can save 56 bytes on every page.

DC> Sure, but it means that ext4 w/ delalloc won't work on lots of
DC> machines....

it does not currenly. but I'm going to implement that. not sure
whether it's worth to have two different codepaths for
block size=page size and block size < page size.

DC> FWIW, how does this mechanism deal with block size < page size?
DC> Don't you have to track delalloc on a block basis rather than
DC> a page basis?
>> I'm still thinking how better to deal with that w/o much code duplication.

DC> Code duplication in ext4, or across all filesystems?

given what Andrew said about moving the code into VFS, it's more
about all filesystems.

thanks, Alex
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